Annual report FOM programme nr. 157 'Two-dimensional semiconductor crystals'

Transcription

1 NWOI Annual report 2016 FOM programme nr. 157 'Two-dimensional semiconductor crystals' Laser-induced metallic to semiconducting transition in a MoS2 field-effect transistor May

2 Content 1. Scientific results Added value of the programme Personnel Publications TWOD TWOD TWOD PhD defences Valorisation, outreach and patents Vacancies... 4 Fact sheet as of 1 January Overview of projects and personnel... 7 Workgroup FOM-D Workgroup FOM-N Workgroup FOM-T Workgroup FOM-T

3 1. Scientific results 2016 In 2016 the first results obtained by the TWOD PhD students and post doc that have become available. Nikos Papadopoulos (TUD) has characterized laser patterned MoS 2 structures that have been immersed in n- butyl lithium. The n-butyl lithium converts the 2H-MoS 2 to a mix of 1T/1T and 2H with ratio depending on the degree of the doping. He also measured the transport properties of MoS 2 flakes encapsulated in boron nitride (using the van der Waals pick up technique). The BN/MoS 2/BN devices showed relatively high mobilities and also effects of quantum interference in the magneto transport measurements. Jaap Kroes (RU) studied the hydrogenation of hexagonal boron nitride (h-bn) using density functional theory based calculations. A first paper on this topic has been published in Hydrogenation of h-bn was found to be a complex process whereby diffusion barriers are significantly altered by the presence of other H atoms and the stability of the chemisorption products may be significantly enhanced by the presence of Stone-Wales defects. This work also formed the basis for our subsequent investigation on proton permeation of 2D membranes which came out in early Rik van Bremen (UT) started with the growth of silicon on WSe 2 and MoS 2. In contrast to germanium, silicon does not grow on top of these transition metal dichalcogenides, but intercalates between the transition metal dichalcogenides layers. A first paper on the growth of silicon on WSe 2 appeared in 2016, whereas a second paper dealing with the growth of silicon on MoS 2 is ready for submission. He also studied the scanning tunnelling microscopy (STM)-induced delamination of MoS 2. Together with the theory group of Katsnelson we now try to understand and explain the experimental observations. Finally, Michal Ochapski (UT) studied h-bn terminated surfaces for the growth of new 2D lattices of the carbon group elements. Two surfaces were investigated: h-bn terminated epitaxial ZrB 2 thin films on Si(111), and h- BN terminated Cu foil. The latter is readily (commercially) available, but turns out to exhibit poor surface quality, although STM studies showed that the surfaces could be cleaned and smoothened to some extent using annealing treatments. Superior h-bn terminated surfaces can be obtained by a combination of plasma nitridation and annealing of ZrB 2 thin films (performed by our collaborators at JAIST, Japan). Post-growth annealing of ultrathin Sn layers deposited onto such surfaces was found to result a new, Sn-related surface reconstruction, using LEED and synchrotron-based PES. The narrow coverage/temperature window in which this occurs has been mapped out, and STM characterization is ongoing. In 2016 two scientific meetings have been organized: a kick-off meeting (March 2016) and a scientific TWOD meeting in Nijmegen (December 2016). Two renowned scientists from field have been invited (Prof. Patrick Vogt, Berlin and Prof. Zeila Zanolli, RWTH Aachen) for these two meetings. 2. Added value of the programme The programme formally started mid 2015 with the appointment of the first PhD student and post doc. However, it should be noted here that immediately after granting of the proposal the first collaborations already started. The collaboration of the Katsnelson group (RU, theory), Kelly group (UT) and the Zandvliet group (UT, experiment) resulted in 2016 into two Physical Review Letters on the germanene/molybdenum disulfide system. These two papers appeared back-to-back in the same issue (T. Amaki, M. Bokdam and P.J. Kelly, Z 2 invariance of Germanene on MoS 2 from first principles, Physical Review Letters 116, (2016) and L. Zhang, P. Bampoulis, A.N. Rudenko, Q. Yao, A. van Houselt, B. Poelsema, M.I. Katsnelson and H.J.W. Zandvliet, Structural and electronic properties of Germanene on MoS 2, Physical Review Letters 116, (2016)). Both papers were featured in Physics ( in an article entitled 'A Good Match for Germanene'. These paper, although formally none of the involved PhD students and post docs were employed at the FOM programme, is at the heart of the TWOD programme. 3. Personnel Three of the four PhD positions are currently filled: Nikos Papadopoulos (June 2015, TUD), Rik van Bremen (January 2016, UT) and Michal Ochapski (March 2016, UT). The fourth PhD position (Brocks/Kelly, UT) will be filled in the coming months (a candidate has already been selected). Currently three of the four PD positions are filled: Jaap Kroes (April 2015, RU), Andrei Lugovski (January 2016, RU) and Qihong Chen (March 2016, RUG). A candidate for the fourth PD position (UT), which was scheduled to - 3 -

4 be filled in 2017, has already been selected. His name is Pantelis Bampoulis and he will start on September 1, We expect that in the autumn of 2017 all the vacant positions will be filled. 4. Publications 14TWOD02 a. Scientific (refereed) publications - J.M.H. Kroes, A. Fasolino, M.I. Katsnelson, Energetics, barriers and vibrational spectra of partially and fully hydrogenated hexagonal boron nitride, Phys. Chem. Chem. Phys. 18, b. Presentations at (inter)national scientific conferences - FOM project meeting on (Nijmegen) Title: Density Functional Based Simulations on the Hydrogenation and Proton, Permeation of Graphene and h-bn (Jaap Kroes). - University of Twente, invited seminar (October 2016) Title: Density functional based calculations of hydrogenated hexagonal Boron Nitride (Jaap Kroes). 14TWOD04 b. Presentations at (inter)national scientific conferences - Flatlands, Lijubliana, Slovenia (July 2016) Title: 'Laser patterning of in-plane MoS 2 heterostructures' (Nikos Papadopoulos). - FOM project meeting on (Nijmegen) Title: Quantum transport in bilayer MoS 2 fabricated via modified van der Waals stacking (Nikos Papadopoulos). 14TWOD07 a. Scientific (refereed) publications - Q. Yao, R. van Bremen and H.J.W. Zandvliet, Growth of silicon on tungsten diselenide, Applied Physics Letters 109, (2016). - L. Zhang, P. Bampoulis, A.N. Rudenko, Q. Yao, A. van Houselt, B. Poelsema, M.I. Katsnelson and H.J.W. Zandvliet, Structural and electronic properties of Germanene on MoS 2, Physical Review Letters 116, (2016). b. Presentations at (inter)national scientific conferences - FOM project meeting on (Nijmegen) Title: Silicon growth on MoS2 and WSe2 (Rik van Bremen). - Germanene: graphene s new little sister (Harold Zandvliet) NanoTR-12 (Istanbul/Turkey, June 2-4, 2016). 5. PhD defences Not applicable yet. 6. Valorisation, outreach and patents The two Physical Review Letters from the Katsnelson/Kelly/Zandvliet groups dealing with germanene on MoS 2 have been featured in various media/journals: - Physics 'A Good Match for Germanene' ( - Technology News 'Right breeding floor for germanene' ( - Science Daily 'Proper breeding ground for germanene' ( 7. Vacancies The fourth and last PhD position (Brocks/Kelly, UT) will be filled in the coming months (a candidate has already been selected). The three remaining PD positions will all be filled in 2017: Andrei Lugovski (January 2017, RU), Qihong Chen, (March 2017, RUG) and Pantelis Bampoulis (September 2017, UT)

5 Fact sheet as of 1 January 2017 FOM /2 datum: APPROVED FOM PROGRAMME Number 157. Title (code) Two-dimensional semiconductor crystals (TWOD) Executive organisational unit BUW Programme management Prof.dr.ir. H.J.W. Zandvliet Duration Cost estimate M 1.6 Concise programme description a. Objectives In this programme we aim to synthesize and characterize two-dimensional materials that have a sizeable band gap and appreciable charge carrier mobilities. We will propose, design, characterize and implement elementary field-effect based electronic devices that rely on two-dimensional semiconductors. Particular attention will be paid to (1) the opening/tuning of a band gap, (2) encapsulation, (3) field-effect characteristics, (4) artificial multilayers and (5) magnetic doping. We will focus on silicene, phosphorene and transition-metal (di)chalcogenides (e.g., molybdenum disulfide), and explore in a concerted and coherent way, new fundamental science and applications of these novel two-dimensional semiconductors. b. Background, relevance and implementation In the past decade a new exciting class of materials has been developed, which is not three-dimensional, but two-dimensional in nature. Graphene is the most famous example of this new class of materials. It exhibits a wealth of exotic and intriguing properties, which has resulted in a myriad of scientific breakthroughs. However, graphene also suffers from a severe drawback: it is gapless, implying that it cannot take over the leading role that silicon plays in the current microelectronic industry. There are several two-dimensional materials such as silicene, phosphorene and transition-metal (di)chalcogenides that have a band gap (or band gap can be opened up in these materials). Two-dimensional semiconductors are very appealing for modern electronics, which is basically two-dimensional, as the functionality of devices is dominated by what occurs at the interfaces of semiconductors. Manipulating charge carrier densities and transport is often hindered rather than assisted by having to use bulk semiconductors. Employing two-dimensional semiconductors would enable to enter a new regime and open doors to exciting new physics and applications. We envisage these two-dimensional semiconductor crystals as the gateway to a wealth of novel and exciting phenomena with a strong potential for technological applications. A balanced and well-chosen arsenal of experimental and theoretical techniques that includes transport measurements, scanning tunneling microscopy & spectroscopy, photoemission electron spectroscopy, low energy electron microscopy and diffraction, near edge X-ray absorption fine structure, photoluminescence and Raman spectroscopy, density functional theory and quantum many body theory calculations will used to address these tantalizing challenges. In the starting phase of the programme, PhD students will pay visits of about 1-2 weeks to the other research groups. In addition, several experimental PhD and postdoc projects are executed in two research groups, the majority in the host group, but another part at the second location. Network meetings are held every

6 months at one of the research groups. The programme leader will organize an international workshop at the start and at the end of the programme in order to give an additional boost to the knowledge level and ambition of the junior scientists (PhD and postdocs) and to cement future networks and collaborations conducive to their further careers. Funding salarispeil cao tot bedragen in k > 2021 Totaal FOM-basisexploitatie FOM-basisinvesteringen Doelsubsidies NWO Doelsubsidies derden Totaal Source documents and progress control a) Original programme proposal: FOM b) Ex ante evaluation: FOM c) Decision Executive Board: FOM Remarks The final evaluation will be based on the self-evaluation report initiated by the programme leader and is foreseen for HO par. HOZB Subgebieden: 50% COMOP, 50% NANO - 6 -

7 Overview of projects and personnel Workgroup FOM-D-44 Leader Organisation Project leader(s) Project (title + number) Prof.dr.ir. H.S.J. van der Zant Delft University of Technology Field-effect devices (14TWOD04) FOM employees on this project Name Position Start date End date N. Papadopoulos PhD 1 June May 2019 Workgroup FOM-N-24 Leader Organisation Project leader(s) Project (title + number) Prof.dr. A. Fasolino Radboud University Nijmegen Structural and thermal properties (14TWOD02) FOM employees on this project Name Position Start date End date J. Kroes WP/T 1 April March 2017 Workgroup FOM-T-36 Leader Organisation Project leader(s) Project (title + number) Prof.dr.ir. H.J.W Zandvliet Twente University Structural and electronic properties (14TWOD07) FOM employees on this project Name Position Start date End date R. van Bremen PhD 31 December 2019 Workgroup FOM-T-43 Leader Organisation Project leader(s) Project (title + number) Dr.ir. M.P. de Jong Twente University Growth, capping and physical properties (14TWOD05) FOM employees on this project Name Position Start date End date M.W. Ochapski PhD 1 March February

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